Aphasia is an acquired neurogenic language disorder resulting from an injury to the brain, most typically the left hemisphere, that affects all language modalities. Aphasia is not a single disorder, but instead is a family of disorders that involve varying degrees of impairment in four primary areas:
- spoken language expression
- spoken language comprehension,
- written expression, and
- reading comprehension.
A person with aphasia often has relatively intact nonlinguistic cognitive skills, such as memory and executive function skills, although these and other cognitive deficits may co-occur with aphasia. Sensory deficits such as auditory and visual agnosia and visual field deficits (e.g., hemianopia or visual field cuts) may also be present.
Because categorizing aphasia subtypes can be difficult, there is debate over the terminology used to classify aphasia. While no single classification system is completely adequate, some common classifications of aphasia are based on the location of brain damage or the patterns of impaired language abilities in fluency of verbal expression, auditory comprehension, repetition, and word retrieval. Sometimes the terms motor aphasia and sensory aphasia (or nonfluent and fluent aphasia) are used. See the common classifications of aphasia adapted from Aphasiology: Disorders and Clinical Practice (Davis, 2007).
It should be noted that a person's symptoms may not fit neatly into a single aphasia type. Further, the initial presenting symptoms can change with recovery, and consequently, the classification that fits most accurately may shift. This is particularly true as a person's communication improves. In addition, symptoms can co-occur with other speech and language impairments such as dysarthria and/or apraxia of speech, which can complicate assessment and treatment.
The outcome of aphasia is difficult to predict given the wide variability of symptoms. Aphasia outcome varies significantly from person to person, depending upon the lesion location and the severity of the brain insult. The most predictive indicator of long-term recovery is initial aphasia severity, along with lesion site and size (Plowman, Hentz, & Ellis, 2011). Other factors that are often considered regarding prognosis include the person's age, gender, education level, and other comorbidities. When examined more closely, however, these factors do not appear to be strong predictors of the extent of recovery.